The present invention relates to an aperture setting device for use with an exposure control device for setting the optimum aperture depending upon the brightness or luminance of a subject.
There have been devised and demonstrated various automatic exposure control devices of the type in which a plurality of aperture setting blades are drivingly coupled to a galvanometer or servomotor so that they are driven to define the optimum aperture or f/number depending upon the brightness of a subject to be photographed. These automatic exposure control devices have a common serious defect that the response of the galvanometer or servomotor to the sudden change in brightness of a subject is so slow that the aperture or f/number set by the aperture setting blades cannot precisely follow the change in brightness of the subject. In the galvanometer or servomotor, the light-weight moving coil or rotor is rotated by a stationary magnetic circuit so that when the moving coil or rotor is stopped at a desired position, it overshoots and rests in position after a considerable time of damping. Therefore, the response to the change in brightness of a subject is further adversely affected. Moreover, the prior art automatic exposure control devices are objectionable in that when the mechanical shock is imparted them, they are easily damaged or malfunction occurs because the ends of the shaft of the moving coil or rotor are sharply pointed in order to reduce the friction as much as possible.